2. Basic anatomy of your computer

Your computer has a processor chip inside it that does the actual
computing. It has internal memory (what DOS/Windows people call
"RAM" and Unix people often call "core"; the Unix
term is a folk memory from when RAM consisted of ferrite-core donuts). The
processor and memory live on the
motherboard,
which is the heart of your computer.

Your computer has a screen and keyboard. It has hard drives and an
optical CD-ROM (or maybe a DVD drive) and maybe a floppy disk. Some of
these devices are run by controller cards that plug
into the motherboard and help the computer drive them; others are run by
specialized chipsets directly on the motherboard that fulfill the same
function as a controller card. Your keyboard is too simple to need a
separate card; the controller is built into the keyboard chassis
itself.

We'll go into some of the details of how these devices work later. For
now, here are a few basic things to keep in mind about how they work
together:

All the parts of your computer inside the case are connected by a
bus.
Physically, the bus is what you plug your controller cards into (the video
card, the disk controller, a sound card if you have one). The bus is the
data highway between your processor, your screen, your disk, and everything
else.

(If you've seen references to ‘ISA’, ‘PCI’,
and ‘PCMCIA’ in connection with PCs and have not understood
them, these are bus types. ISA is, except in minor details, the same bus
that was used on IBM's original PCs in 1980; it is no longer used.
PCI, for Peripheral Component Interconnection, is the bus used on most
modern PCs, and on modern Macintoshes as well. PCMCIA is a variant of ISA
with smaller physical connectors used on laptop computers.)

The processor, which makes everything else go, can't actually see any of
the other pieces directly; it has to talk to them over the bus. The only
other subsystem that it has really fast, immediate access to is memory (the
core). In order for programs to run, then, they have to be in
core (in memory).

When your computer reads a program or data off the disk, what actually
happens is that the processor uses the bus to send a disk read request
to your disk controller. Some time later the disk controller uses the
bus to signal the processor that it has read the data and put it in a
certain location in memory. The processor can then use the bus to look
at that data.

Your keyboard and screen also communicate with the processor via the
bus, but in simpler ways. We'll discuss those later on. For now, you know
enough to understand what happens when you turn on your computer.